Zero COVID worked for some countries – but high vaccine coverage is now key

Since the start of the pandemic, several countries have adopted a zero-COVID strategy, aiming to eradicate COVID within their borders. Faced with the highly transmissible delta variant, many are now abandoning it.

New Zealand is the latest country to abandon the zero-COVID approach, following hard on the heels of Vietnam and Australia.

Vietnam was once hailed as a zero-COVID success, but it has recently experienced a sharp rise in deaths. Despite a population of 97 million, Vietnam managed to keep cases below 3,000 until May 2021, when the delta variant started to spread internationally. By October, it had 800,000 cases, and COVID deaths had risen from 35 to 20,000.

China, Hong Kong and Taiwan are the remaining zero-COVID holdouts. How long they will continue with this strategy is anyone’s guess.

Different approaches

Countries that quickly closed their borders, once initial reports of a new epidemic emerged from China in January 2020, were able to put zero-COVID strategies in place and keep death rates low. Effective border quarantines were easiest for island nations. But countries with strong central political control, such as China, were also able to implement this strategy.

Control strategies lay on a spectrum, from a laissez-faire and chaotic approach characterized by denial, in the case of Brazil; and laissez-faire, civil libertarian approach of relying on disease-induced herd immunity, in the case of Sweden. To a zero-COVID approach on the other end of the spectrum – as pursued by China.

There can be little doubt that countries that adopted a zero-COVID strategy saved thousands – if not hundreds of thousands – of lives. The most important lesson, however, is not to find and adhere to one strategy, but to steadily follow the science.

Infectious diseases and our responses to them have both evolved. Simple facts around the transmission power of the delta variant show how the ability of SARS-CoV-2 to mutate in conditions of rampant infection has been a gamechanger.

The viral load, which is the concentration of the virus in the throat and nose, is 1,000 times higher with delta than with the original virus. The reproductive number, which is the average number of people that one infected person will pass on the virus to, averages 5.1 for delta, compared with 2.8 with the initial virus. This is the difference between a possible 200 extra infections transmitted from a single case in three weeks, compared with 15 new infections with the original virus.

Zero-COVID has been effective at preventing deaths and allowing a certain level of normality within national borders in countries that moved rapidly to shut their borders, and where the geographical, political and economic factors were favourable. No countries in Europe or the Americas attempted it. But the huge jump in virus transmissibility and the swift development of highly effective vaccines has forced changes in the response.

A high price to pay

The standout countries now are those, like Singapore, that kept case numbers and deaths low and moved quickly to reach high vaccine coverage levels. New Zealand and Australia, at 40%-50% coverage, are playing vaccine catchup and are at risk. China has reached 75%, but Taiwan and Vietnam are lagging far behind.

COVID disease and transmission in children are uncommon. Therefore, the critical target for countries to reach is over 90% coverage in adults, which Denmark, Ireland and Portugal have reached. But vaccine breakthrough – that is, fairly mild infections in those fully vaccinated – is now common. And countries have started booster vaccine programmes to reinforce immunity in the elderly and vulnerable.

Taiwan successfully controlled its first big COVID wave between May and July 2021. And daily cases in Hong Kong have been in single figures since April. But they need to move quickly to high vaccination coverage levels before these strategies start to crumble. Unless a new generation of vaccines can provide much higher protection, regardless of emerging variants, the zero-COVID era will not return. The exception will be where countries can combine high vaccine coverage, virtually complete isolation, and rapid and draconian lockdowns when viruses creep through these barriers. Perhaps China, alone, can achieve this.

If COVID cases and deaths are the only measures of success, then China ranks top overall due to its ability to control personal lives and public behavior, and its ability to shift quickly to a vaccine-led strategy. However, people living in democracies that guarantee a high degree of personal liberty might reckon that the cost of an epidemic-free society is too high.

(By Ruairi Brugha, Emeritus Professor of Public Health and Epidemiology, RCSI University of Medicine and Health Sciences)